Apparatus and method for single-crystal casting

ABSTRACT

Apparatus and method for producing single-crystal parts having a relative large dimension at right angles to the major axis, for example, discs or plates, or rods or ingots having a large crosssectional area.

United States Patent [72] Inventors Stephen M. Copley Madison;

Anthony F. Giamei, Middletown; Merton F. l-lornbecker, Woodbury; Bernard H. Kear, Madison, all of Conn.

Mar. 13, 1969 Dec. 7, 197 i United Aircraft Corporation East Hartford, Conn.

Appl. No. Filed Patented Assignee APPARATUS AND METHOD FOR SINGLE CRYSTAL CASTING 9 Claims, 5 Drawing Figs.

U.S. Ci 164/60, 164/338, 164/361 Int. Cl 822d 25/06 [50] Field of Search l64/60, 122,125,127, 338, 353. 361; i48/l.6

[56] References Cited UNITED STATES PATENTS 3,385,346 5/l968 Fleck l64/l 21 3,494,709 2/l970 Piearcey 4 l 6/232 3,538,981 ll/l970 Phipps l64/60 3.5 I 5,205 6/ i 970 Wickstrand l64/353 Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel A!!0rne v-Charles A. Warren ABSTRACT: Apparatus and method for producing singlecrystal parts having a relative large dimension at right angles to the major axis, for example, discs or plates. or rods or ingots having a large cross-sectional area,

PATENTED 11H: 7 Ian SHEET 2 UF 3 v v a/ 428 4, 3/4

W47 Waxy PATENTEU DEC 7197:

sum 3 OF 3 APPARATUS AND METHOD FOR SINGLE-CRYSTAL CASTING SUMMARY OF INVENTION One feature of the invention is an arrangement by which to cast single crystal articles having a relative large dimension at right angles to the major axis, thus necessitating a large horizontal dimension in the mold cavity. One particular feature is a method and apparatus by which to cast discs and the like in a mold with the disc axis extending vertically to obtain the desired crystalline orientation within the mold.

One feature of the invention is the production of single crystal cast parts made from any of the well-known high-temperature superalloys, examples of which are given in Ver- Snyder U.S. Pat. No. 3,260,505, in which the articles has a large dimension substantially at right angles to the [l]orientation, such as discs, large diameter rods or large cross-sectional ingots.

This invention is in certain respects a modification or improvement on Sink and Rear, Ser. No. 714,743 in that parts of large horizontal dimension within the mold can be successfully cast free of spurious crystals and in that the restriction at the lower end of the article casting cavity is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view of a mold and associated devices showing an embodiment of the invention.

FIG. 2 is a horizontal sectional view of the filling tube.

FIG. 3 is a vertical sectional view as in FIG. 1 of a modification.

FIG. 4 is a view similar to FIG. 2 of another modification.

FIG. 5 is a transverse sectional view through a cast disc showing a preferred crystalline orientation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. I the invention is shown in apparatus for producing an ingot or cylinder of a single crystal, the cylinder having a relatively large radius and a substantial height. The crystalline structure enlarged five times is shown in FIG. 5 from which it is clear that the l00]orientati0n is axially of the cylinder (vertically in the mold) and the dendritic growth in the horizontal plane is symmetrical throughout the ingot or cylinder.

As shown in FIG. I, a chill plate having cooling means therein supports a cylindrical sleeve 12 which encloses the article (ingot) forming mold 14. This mold is supported above and in spaced relation to the chill plate by support elements I6 and the walls thereof are spaced from the sleeve 12. The mold is cylindrical, having a diameter nearly as large as the surrounding sleeve and a substantial height. The top of the mold is closed and the bottom has a filling opening 17. The mold is preferably a shell mold and is somewhat porous for the escape of air therein during filling of the mold. The mold may be made by the lost-wax process, for example, and may be relatively thin since as the mold is being filled the level of the metal inside and outside the mold is substantially the same.

Extending downwardly from the filling 17 is a helical tube I8 by which a single crystal for growth into the mold is selected. Although this is described and shown as a helical tube in FIGS. 1 and 3 it need only be a tube with enough changes in direction to exclude all but one grain. Thus a bent tube with enough changes in direction in the horizontal plane for producing at least a change in direction of 180 would be adequate. The tube itself preferably has its centerline continuously on an uphill. slope and is large enough in diameter to permit a relatively free flow of the molten alloy upward into the mold. A helical tube with a vertical axis perpendicular to the chill is obviously the simplest configuration and if it extends at least 180 it serves to exclude all but one crystal without the need of the very small restriction at the bottom of the mold that has been used to produce a single-crystal growth in the article forming mold. The bottom end of tube 18 is spaced from the chill plate, as shown.

As shown in FIG. 2 the radius of curvature of the helix is greater than the radius of the tube itself so that there is no possibility for direct vertical growth of a crystal from the chill plate through the tube.

The bottom wall of the mold forms a relatively small acute angle to the horizontal and is relatively close to the chill plate, as shown. The small slope to this bottom wall helps to avoid nucleation of undesired crystals on this wall. With this small slope angle, the horizontal dimension of the mold increases rapidly and, thus a casting with a large horizontal dimension may be produced with only a single crystal. Although the drawing shows a mold for a cylinder, it will be understood that other articles having a large horizontal dimension may be produced by this technique.

The top end of the shell or sleeve 12 has a cap 20 preferably of insulating material to minimize the loss of heat from the alloy as it is cooled and a central opening 22 in the cap permits the positioning of the pouring sprue 24. a

In operation, the assembly shown is positioned in a heating chamber so that the mold and shell 'may be heated to a temperature above the melting point of the alloy. The chamber is preferably a vacuum chamber so that the casting may be done in a vacuum. The technique of heating the mold and casting the alloy therein follows that described in general in Ver- Snyder US. Pat. No. 3,260,505 and in Piearcey US. Pat. No. 3,494,709. when the mold and shell are at the desired temperature, the alloy is poured into the sprue and flows around the mold to fill the shell and to flow upwardly through the tube 18 into the mold. The shell and mold are filled to approximately the line 26, assuring that the effective portion of the mold is filled. The chill plate then becomes effective and begins the growth of directionally solidified grains into and around the tube 18. The directionally solidified grains extend at right angles to the chill plate and have a [l00]orientation. The few grains that enter the tube 18 are also vertically oriented, and as growth continues through the turns of the tube all but one grain is excluded and this single grain grows into the article mold.

The solidification within and outside the tube occurs at substantially the same rate and thus the liquid-solid interface remains close to the horizontal. When solidification within the mold begins the liquid-solid interface moves vertically only a short distance as solidification expands horizontally to the full horizontal dimension of the mold. Thus a minimum of material is solidified as the horizontal solidification occurs and a minimum of heat extraction is necessary during this portion of the cooling process. As a result, a high thermal gradient is maintained throughout and the dendritic structure will be on a fine scale with a minimum of porosity. It will be understood that the thermal gradient is preferably obtained by reducing the heating of the mold and shell gradually from bottom to top as described in Piearcey US. Pat. No. 3,494,709.

Referring to FIG. 3 the invention is shown in this embodiment in the production of a relatively fiat disc such as could be used as a turbine disc if cast of one of the strong high-temperature alloys. As shown, the chill plate 10', having means for cooling it, supports the cylindrical sleeve 12' which encloses the article-forming mold 14. The latter is suitably supported above the chill plate by supports I6'and is spaced above the chill plate and also spaced from the sleeve I2. This mold has a closed top and the filling opening 17' at the bottom and is generally of the type known as a shell mold made for example by the loss-wax process. As in FIG. 3 the mold wall may be much thinner than in the usual techniques since, as will appear, the wall constitutes merely a baffle and molten alloy on both inside and outside of the mold balances the pressure on the wall.

Attached to the filing opening 17 and extending downwardly toward the chill plate is the helical or spiral tube 18' through which the mold is filled.

In the arrangement shown in FIG. 4, the same apparatus is used as in FIG. 1, with the addition of a ring of insulating material 30 under and spaced from the mold and surrounding the spiral tube 18". This reduces the volume to be filled by molten alloy and makes a more precise control of the thermal gradient during the solidification of the alloy along the bottom wall of the mold 14''. The insulation 30 is protected from the molten alloy by an inner shell 32 and the supports 16" rest on this shell 32, as shown. The top surface of the mold 14" may have a ring of filer cement 34 thereon, in spaced relation to the inner shell 32, to reduce the amount of alloy needed to fill the apparatus to the desired level 26". This arrangement is operated in much the same manner as above described.

Although the description is directed to an annular cast article it will be understood that the invention is equally applicable to other shapes and configurations, even such as horizontally positioned molds for tubes, rods or bars and the like where the longitudinal axis may extend at a small acute angle to the horizontal and where the resulting crystalline orientation is desired or acceptable in the cast part. Obviously several individual cast parts may be produced simultaneously where the several cast article molds may be arranged in a ring communicating with the upper end of the helical tube.

We claim:

1. Apparatus for casting single-crystal articles having a large horizontal dimension including:

a. a shell for the reception of molten alloy in the cavity defined by the shell and having an open bottom,

2. A chill plate on which said shell is positioned,

3. an article-forming mold also for the reception of molten alloy in the cavity defined by said article mold and located within said shell and spaced horizontally therefrom, said mold having a relatively flat bottom spaced above and making an acute angle with the surface of the chill plate, said bottom having an opening at the lowermost portion, and

. a nonrectilinear tube extending downwardly from said bottom toward the chill plate, said tube communicating with both the article cavity and the shell cavity, said tube serving to select a single crystal to grow into the articleforming mold said tube forming a continuously upwardly sloping path nd at least a portion having a curvature and extending at least 180 about a substantially vertical axis with the passage in said tube spaced from said vertical axis throughout said curved portion.

2. Apparatus as in claim 1 in which the tube is in the form of a vertically positioned helix.

3. Apparatus as in claim 1 in which the shell has a bottom wall extending inwardly from the periphery of the shell in spaced relation to and below the bottom of the article-forming mold except for the portion adjacent to and enclosing the tube which portion is open to rest on the chill plate and define a growth zone below and around said tube.

4. The method of casting single-crystal articles having a major horizontal dimension which involves placing a shell having an open bottom on a chill plate, positioning an article mold within the shell with the bottom wall in spaced relation above the chill plate and with a curved tube extending downwardly from the bottom of said article mold at the bottom thereof toward the chill plate with the bottom end of the tube spaced from the chill plate, heating the shell and article mold to a temperature above the melting point of the alloy, pouring the alloy into the molds to fill the article mold and to surround the article mold with molten alloy, extending heat from the alloy within the molds through the chill plate while keeping the molds above the chill plate hot and gradually reducing the heat supplied to the mold from bottom to top to produce a thermal gradient within the molds with the cooling eflect'controlled to produce directionally solidified grains growing vertically from the chill plate, and in which the curved tube forms a continuously upwardly sloping passage which is curved through at least 180 and selects a single crystal from the directionally solidified grains to grow into the article mold the radius of curvature being greater than the radius of the tube.

5. The method as claimed in claim 4 including the step of controlling the heat reduction in the mold and the extraction of heat by the Chill plate to maintain a substantially horizontal solid-liquid interface within and outside the article mold during solidification.

6. Apparatus for casting single-crystal articles including a shell having an open bottom and adapted to be filled with molten alloy, a chill plate on which the shell is positioned, an article mold within the shell and spaced at least in part from the shell, said mold having a bottom opening above and spaced from the chill plate and located at the lowermost point of the mold, and a curved tube extending downwardly from said bottom opening toward the chill plate, said tube being open at the top end to the cavity within the article mold and at its bottom end to the space within the shell, and said tube being curved about a substantially vertical axis, the radius of the curve being greater than the radius of the tube and said tube defining a continuously upwardly sloping passage, serving to select a single crystal from the solidifying alloy within the shell.

7. Apparatus as in claim 6 in which the tube has a relatively large cross-sectional area and is in the form substantially of a helix.

8. Apparatus as in claim 6 in which the tube has a change in horizontal direction of at least between the bottom end and its connection to the mold.

9. Apparatus for casting single-crystal articles, including a chill plate,

an article mold positioned above and in spaced relation to the chill plate and having a bottom wall with an opening therein nonrectilinear tube extending downwardly toward the chill plate from said bottom wall and in communication with said opening therein, and with an open lower end located in spaced relation to and above the chill plate, and a growth zone communicating with the lower end of said tube and having an open bottom end resting on the chill plate, said tube having a portion thereof continuously curved about a substantially vertical axis and forming a continuously upwardly sloping path for the molten alloy in said portion between the bottom and top of the tube, the radius of curvature of the tube about the vertical axis being greater than the radius of the tube.

i i i t i 

1. Apparatus for casting single-cRystal articles having a large horizontal dimension including:
 1. a shell for the reception of molten alloy in the cavity defined by the shell and having an open bottom,
 2. A chill plate on which said shell is positioned,
 3. an article-forming mold also for the reception of molten alloy in the cavity defined by said article mold and located within said shell and spaced horizontally therefrom, said mold having a relatively flat bottom spaced above and making an acute angle with the surface of the chill plate, said bottom having an opening at the lowermost portion, and
 4. a nonrectilinear tube extending downwardly from said bottom toward the chill plate, said tube communicating with both the article cavity and the shell cavity, said tube serving to select a single crystal to grow into the article-forming mold said tube forming a continuously upwardly sloping path and at least a portion having a curvature and extending at least 180* about a substantially vertical axis with the passage in said tube spaced from said vertical axis throughout said curved portion.
 2. Apparatus as in claim 1 in which the tube is in the form of a vertically positioned helix.
 2. A chill plate on which said shell is positioned,
 3. an article-forming mold also for the reception of molten alloy in the cavity defined by said article mold and located within said shell and spaced horizontally therefrom, said mold having a relatively flat bottom spaced above and making an acute angle with the surface of the chill plate, said bottom having an opening at the lowermost portion, and
 3. Apparatus as in claim 1 in which the shell has a bottom wall extending inwardly from the periphery of the shell in spaced relation to and below the bottom of the article-forming mold except for the portion adjacent to and enclosing the tube which portion is open to rest on the chill plate and define a growth zone below and around said tube.
 4. a nonrectilinear tube extending downwardly from said bottom toward the chill plate, said tube communicating with both the article cavity and the shell cavity, said tube serving to select a single crystal to grow into the article-forming mold said tube forming a continuously upwardly sloping path and at least a portion having a curvature and extending at least 180* about a substantially vertical axis with the passage in said tube spaced from said vertical axis throughout said curved portion.
 4. The method of casting single-crystal articles having a major horizontal dimension which involves placing a shell having an open bottom on a chill plate, positioning an article mold within the shell with the bottom wall in spaced relation above the chill plate and with a curved tube extending downwardly from the bottom of said article mold at the bottom thereof toward the chill plate with the bottom open end of the tube spaced from the chill plate, heating the shell and article mold to a temperature above the melting point of the alloy, pouring the alloy into the molds to fill the article mold and to surround the article mold with molten alloy, extending heat from the alloy within the molds through the chill plate while keeping the molds above the chill plate hot and gradually reducing the heat supplied to the mold from bottom to top to produce a thermal gradient within the molds with the cooling effect controlled to produce directionally solidified grains growing vertically from the chill plate, and in which the curved tube forms a continuously upwardly sloping passage which is curved through at least 180* and selects a single crystal from the directionally solidified grains to grow into the article mold the radius of curvature being greater than the radius of the tube.
 5. The method as in claim 4 including the step of controlling the heat reduction in the mold and the extraction of heat by the chill plate to maintain a substantially horizontal solid-liquid interface within and outside the article mold during solidification.
 6. Apparatus for casting single-crystal articles including a shell having an open bottom and adapted to be filled with molten alloy, a chill plate on which the shell is positioned, an article mold within the shell and spaced at least in part from the shell, said mold having a bottom opening above and spaced from the chill plate and located at the lowermost point of the mold, and a curved tube extending downwardly from said bottom opening toward the chill plate, said tube being open at the top end to the cavity within the article mold and at its bottom end to the space within the shell, and said tube being curved about a substantially vertical axis, the radius of the curve being greater than the radius of the tube and said tube defining a continuously upwardly sloping passage, serving to select a single crystal from the solidifying alloy within the shell.
 7. Apparatus as in claim 6 in whIch the tube has a relatively large cross-sectional area and is in the form substantially of a helix.
 8. Apparatus as in claim 6 in which the tube has a change in horizontal direction of at least 180* between the bottom end and its connection to the mold.
 9. Apparatus for casting single-crystal articles, including a chill plate, an article mold positioned above and in spaced relation to the chill plate and having a bottom wall with an opening therein, a nonrectilinear tube extending downwardly toward the chill plate from said bottom wall and in communication with said opening therein, and with an open lower end located in spaced relation to and above the chill plate, and a growth zone communicating with the lower end of said tube and having an open bottom end resting on the chill plate, said tube having a portion thereof continuously curved about a substantially vertical axis and forming a continuously upwardly sloping path for the molten alloy in said portion between the bottom and top of the tube, the radius of curvature of the tube about the vertical axis being greater than the radius of the tube. 